The invention relates to a magnetic bearing apparatus and to a method for operating the same in accordance with the preamble of claim 19.
It is known from EP 0 612 928A to use active magnetic bearings for the contact-free journalling of rotors. The principle of the active magnetic bearing is based on the attractive force of regulatable electromagnets on a ferromagnetic rotor. In order to determine the position of the rotor in the radial direction, three U-shaped electromagnets are distributedly arranged over the periphery of the rotor. These three magnet pairs form a so-called radial bearing. In a manner similar to a ball bearing, the radial bearing can hold the rotor fixed at one location in a plane (x-y direction). Since a tilting of the rotor must often also be prevented, the latter is preferably held by two radial bearings arranged at different locations.
This known magnetic bearing apparatus has the disadvantage that the electromagnets are designed in the shape of a U. Therefore this bearing apparatus has a larger number of pole changes over its periphery, which causes increased eddy current losses. A further disadvantage of the known bearing apparatus is to be seen in the fact that the electromagnets are specially manufactured and correspondingly expensive; and in that an individual, special power amplifier is required for each U-shaped electromagnet so that a total of three separate direct current controllers are required for the operation of a radial magnetic bearing.